Letting other users stop/restart simple bash daemons – use signals or what?

Question

I have a web server where I run some slow-starting programs as daemons. These sometimes need quick restarting (or stopping) when I recompile them or switch to another installation of them.

Inspired by http://mywiki.wooledge.org/ProcessManagement, I'm writing a script called daemonise.sh that looks like

#!/bin/sh
while :; do
    ./myprogram lotsadata.xml
    echo "Restarting server..." 1>&2
done

to keep a "daemon" running. Since I sometimes need to stop it, or just restart it, I run that script in a screen session, like:

$ ./daemonise.sh & DPID=$!
$ screen -d

Then perhaps I recompile myprogram, install it to a new path, start the new one up and want to kill the old one:

$ screen -r
$ kill $DPID
$ screen -d

This works fine when I'm the only maintainer, but now I want to let someone else stop/restart the program, no matter who started it. And to make things more complicated, the daemonise.sh script in fact starts about 16 programs, making it a hassle to kill every single one if you don't know their PIDs.

What would be the "best practices" way of letting another user stop/restart the daemons?

I thought about shared screen sessions, but that just sounds hacky and insecure. The best solution I've come up with for now is to wrap starting and killing in a script that catches certain signals:

#!/bin/bash
DPID=
trap './daemonise.sh & DPID=$!' USR1
trap 'kill $DPID' USR2 EXIT

# Ensure trapper wrapper doesn't exit:
while :; do
    sleep 10000 & wait $!
done

Now, should another user need to stop the daemons and I can't do it, she just has to know the pid of the wrapper, and e.g. sudo kill -s USR2 $wrapperpid. (Also, this makes it possible to run the daemons on reboots, and still kill them cleanly.)

Is there a better solution? Are there obvious problems with this solution that I'm not seeing?

(After reading Greg's Bash Wiki, I'd like to avoid any solution involving pgrep or PID-files …)

Answer 1

I recommend a PID based init script. Anyone with sudo privileged to the script will be able to start and stop the server processes.

Answer 2

On improving your approach: wouldn't it be advisable to make sure that your sleep command in sleep 10000 & wait $! gets properly terminated if your pidwrapper script exits somehow?

Otherwise there would remain a dangling sleep process in the process table for quite some time.

Similarly, wouldn't it be cleaner to terminate myprogram in daemonise.sh properly on restart (i. e. if daemonise.sh receives a TERM signal)?

In addition, it is possible to suppress job notification messages and test for pid existence before killing.

#!/bin/sh
# cat daemonise.sh

# cf. "How to suppress Terminated message after killing in bash?",
# http://stackoverflow.com/q/81520

trap '
   echo "server shut down..." 1>&2
   kill $spid1 $spid2 $spid3 &&
      wait  $spid1 $spid2 $spid3 2>/dev/null
   exit
' TERM

while :; do
    echo "Starting server..." 1>&2
    #./myprogram lotsadata.xml
    sleep 100 &
    spid1=${!}
    sleep 100 &
    spid2=${!}
    sleep 100 &
    spid3=${!}
    wait
    echo "Restarting server..." 1>&2
done

#------------------------------------------------------------

#!/bin/bash
# cat pidwrapper

DPID=

trap '
   kill -0 ${!} 2>/dev/null && kill ${!} && wait ${!} 2>/dev/null
   ./daemonise.sh & DPID=${!}
' USR1

trap '
   kill -0 ${!} 2>/dev/null && kill ${!} && wait ${!} 2>/dev/null
   kill -0 $DPID 2>/dev/null && kill $DPID && wait ${DPID} 2>/dev/null
' USR2 

trap '
   trap - EXIT
   kill -0 $DPID 2>/dev/null && kill $DPID && wait ${DPID} 2>/dev/null
   kill -0 ${!} 2>/dev/null && kill ${!} && wait ${!} 2>/dev/null
   exit 0
' EXIT

# Ensure trapper wrapper does not exit:
while :; do
    sleep 10000 & wait $!
done

#------------------------------------------------------------

# test

{
wrapperpid="`exec sh -c './pidwrapper & echo ${!}' | head -1`"
echo "wrapperpid: $wrapperpid"
for n in 1 2 3 4 5; do
   sleep 2
   # start daemonise.sh
   kill -s USR1 $wrapperpid 
   sleep 2
   # kill daemonise.sh
   kill -s USR2 $wrapperpid 
done
sleep 2
echo kill $wrapperpid
kill $wrapperpid
}